Coagulation Factor X, also known as FX, F10, Eponym Stuart-Prower factor, and thrombokinase, is a vitamin K-dependent plasma protease that activates thrombin. Initially synthesized in the liver as a single-chain precursor, FX is activated by both intrinsic and extrinsic pathways to form activated FX (FXa), consisting of disulfide bond-linked light and heavy chains. The light chain contains γ-carboxyglutamic acid (Gla) domains and two epidermal growth factor-like (EGF-like) domains, while the heavy chain corresponds to the serine protease domain. FXa contributes to the action of prothrombin complex concentrate and has been identified as an active component in factor eight bypassing activity (FEIBA). FEIBA can be used to treat hemophilia patients who develop inhibitory antibodies against FVIII or FIX.
While FX can be purified from human plasma or produced recombinantly, only in its activated state (FXa) does it affect the blood coagulation process. This activation results from cleavage of the Arg52-Ile53 peptide bond in the heavy chain of FX, releasing the activation peptide. Standard methods of FX activation typically employ exogenous agents such as proteases.